The Electric Exhaust Gas Recirculation(EGR) System Monitor is an on-board strategy designed to test the integrity and flow characteristics of the EGR system. The monitor is activated during EGR system operation and after certain base engine conditions are satisfied. Input from the Engine Coolant Temperature (ECT) , or Cylinder Head Temperature (CHT) , Intake Air Temperature (IAT) , Throttle Position (TP) ,Crankshaft Position (CKP) , Mass Air Flow (MAF), and Manifold Absolute Pressure (MAP) sensors is required to activate the EGR System Monitor. Once activated, the EGR System Monitor will perform each of the tests described below during the engine modes and conditions indicated. Some of the EGR System Monitor tests are also performed during on demand self-test

The Stepper Motor EGR Monitor consists of an electrical and functional test that checks the stepper motor and the EGR system for proper flow. The Powertrain Control Module (PCM) controls the EGR valve by commanding from 0 to 52 discreet increments or "steps" to get the valve from fully closed to fully open. The stepper motor electrical test is a continuous check of the four electric stepper motor coils and circuits to the PCM. A malfunction is indicated if an open circuit, short to power, or short to ground has occurred in one or more of the stepper motor coils I circuits for a calibrated period of time. If a malfunction has been detected, the EGR system will be disabled, setting the Key On Engine Running (KOER) , and Cont. P0403 Diagnostic Trouble Code (DTC) . Additional monitoring will be suspended for the remainder of the driving cycle, or until the next engine startup.

After the vehicle has warmed up and normal EGR rates are being commanded by the PCM, the EGR flow check is performed. The flow test is performed once per drive-cycle when a minimum amount of EGR is requested and the remaining entry conditions required to initiate the test are satisfied. If a malfunction is detected, the EGR system as well as the EGR monitor is disabled until the next engine startup.

The EGR flow test is done by observing the behavior of two different values of MAP - the analog MAP sensor reading, and inferred MAP (MAP calculated from the Mass Air Flow Sensor, throttle position, rpm, etc.). During normal, steady-state operating conditions, EGR is intrusively commanded ON to a specified percentage. Then, EGR is commanded OFF. If the EGR system is working properly, there is a significant difference in both the observed and the calculated values of MAP, between the EGR-ON and the EGR-OFF states.

When the flow test entry conditions have been satisfied, EGR is commanded to flow at a calibrated test rate (about 10%). At this time, the value of MAP is recorded (EGR-ON MAP). The value of inferred MAP EGR-ON MAP is also recorded. Next the EGR is commanded off (0%). Again, the value of MAP is recorded (EGR-OFF MAP). The value of EGR-OFF IMAP is also recorded. Typically, seven such ON/OFF samples are taken. After all the samples have been taken, the average EGR-ON MAP, EGR-ON IMAP, EGR-OFF MAP and EGR-OFF IMAP values are stored.

Next, the differences between the EGR-ON and EGR-OFF values are calculated:

If the sum of MAP-delta and IMAP-delta exceeds a maximum threshold or falls below a minimum threshold, a P0400 (high or low flow malfunction) is registered.

As an additional check, if the EGR-ON MAP exceeds a maximum threshold (BARO - a calibrated value), a P0400 low flow malfunction is registered. This check is performed to detect reduced EGR flow on systems where the MAP pickup point is not located in the intake manifold, but is located just upstream of the EGR valve in the EGR delivery tube.

NOTE: BARO is inferred at engine startup using the KOEO MAP sensor reading. It is updated during high, part-throttle or high rpm engine operation.

If the inferred ambient temperature is less than 20°F (-7°C) , greater than 130°F (54°C) , or the altitude is greater than 8,000 feet (BARO <22.5" Hg) , the EGR flow test cannot be reliably done. In these conditions, the EGR flow test is suspended and a timer starts to accumulate the time in these conditions. If the vehicle leaves these extreme conditions, the timer starts decrementing, and if conditions permit, will attempt to complete the EGR flow monitor. If the timer reaches 500 seconds , the EGR flow test is disabled for the remainder of the current driving cycle and the EGR Monitor I/M Readiness bit will be set to a "ready" condition.

A DTC of P1408, like the P0400, will indicate a EGR flow failure (outside the minimum or maximum limits) but is only set during the KOER self test. The P0400 and P0403 are Malfunction Indicator Lamp(MIL) codes, the P1408 is a non-MIL code.